Core Mechanics can get complicated.

I almost take for-granted how complicated the basic mechanics can be:

Determine relevant Scores or Stats for the roll. This has a lot of implied knowledge. They can be intuitive but when you go down to nitty-gritty there are counter intuitive exceptions to everything and there are ways to frame and approach a problem or challenge.

It gets complicated since there are so many ways to frame the scene, narrative, problem, challenge, and situation and the practice that comes in rearranging Facts to frame something in a manipulative way. It may lead down the rabbit hole of Non-Fiction Writing techniques, Cognitive Biases, Arguments, and even (legal) Objections.

Determine the Situational Modifiers or Scope of Objective of the roll. Determine if the Character has any relevant modifiers from his capabilities, the environmental's or timing's or circumstantial modifiers, and then the Scope of the objective - relative to the resources and time that an action or roll.

One thing that is not usually comes up unless the GM plays Hard Mode is going into the details of the Cost or Opportunity Cost of the Action. Does it consume time, patience of another person or relationship credit, and consumable materials and how each attempt alters the circumstances.

Determine the Consequences of the Roll. If failure, success, or set backs happen. There is the Game's System way to resolve it and there is the best way to resolve it based on the story, the player, the party, and the long game of enjoying the hobby.

Then there is elements of Risk and Chance. if you've heard of a GM who killed a PC on rolling a 1 lighting a torch on a D20, after a basic review on Risk (reading wikiarticles on Probablity, OSHA, and system processes) this becomes something someone more informed would not do. And by Informed this can mean 3000-30k worth of words bits of data of Informed.

Something as Basic as Core or Basic Mechanics can get pretty complicated. so my Gming gdoc keeps getting longer